Current limiting circuit for a brushless DC motor

(19)

(11)

EP 1 271 758 A3

(12)	EUROPEAN PATENT APPLICATION

(88)	Date of publication A3:
	10.12.2003 Bulletin 2003/50

(43)	Date of publication A2:
	02.01.2003 Bulletin 2003/01

(21)	Application number: 02405533.7

(22)	Date of filing: 25.06.2002

(51)	International Patent Classification (IPC)⁷: H02P 6/00, H02P 6/20, H02P 1/46

(84)	Designated Contracting States:
	AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE TR
	Designated Extension States:
	AL LT LV MK RO SI

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Priority:

25.06.2001 JP 2001191384

(71)	Applicant: MINEBEA CO., LTD.
	Kitasaku-gun, Nagano-ken (JP)

(72)	Inventor:
	Xi, Junnan, c/o Minebea Co., Ltd. Miyota-machi, Kitasaku-gun, Nagano-ken (JP)

(74)	Representative: Patentanwälte Schaad, Balass, Menzl & Partner AG
	Dufourstrasse 101 Postfach 8034 Zürich 8034 Zürich (CH)

(54)	Current limiting circuit for a brushless DC motor

(57) There is provided a current limiting circuit to eliminate any harsh grating noise attributable to the decrease in an ON-OFF frequency of an electrified current from a normal range, for example, below 1 kHz when starting a brushless DC fan motor. In the current limiting circuit to limit the current by shutting off field coils to be electrified for a period in which the control voltage exceeds the reference voltage by the output signal of a comparator in which a current-detecting resistor is interposed in electrified passages of the field coils of the brushless DC fan motor to compare the voltage according to the voltage produced across the current-detecting resistor as the control voltage with the reference voltage according to the current to be limited when the motor is started or the like, a differential amplifier is interposed between the current-detecting resistor and the comparator to improve the comparative accuracy between the control voltage with the reference voltage in the comparator so that the accuracy is not easily affected by malfunction factors.

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